ECG of the Month: A 44-Year-Old Woman with History of HTN and Nonischemic Cardiomyopathy Presents to ED

A 44-year-old woman with history of hypertension and nonischemic cardiomyopathy presents to the emergency department (ED) with palpitations consistent of a fluttering sensation in her chest, accompanied by dizziness, lightheadedness and fatigue.

The blue dots in Figure 2 indicate sinus beats. The red dots are blocked premature atrial contractions that occur when the AV node is still in the absolute refractory period (ARP) and has not yet recovered. The P wave in the blocked PACs is different than during sinus rhythm; therefore, Answer choice A is incorrect as this is not second degree AV block.

PACs with aberrancy occurs when the PAC arrives to His-Purkinje system when one of its branches is in ARP or the relative refractory period (RRP).

The green dot represents PAC with right bundle branch block (RBBB) pattern, since the PAC conducts before the recovery of the right bundle from its ARP. The lime green dot represents a PAC with incomplete RBBB because the right bundle is in RRP and has partially recovered. This is eponymously known as Ashman's phenomenon, which happens as a sequence of a long-short cycle, leading to aberrancy in the premature beat.1

The purple dot is a PAC with left bundle branch block (LBBB), since the PAC conducts before the recovery of the left bundle from its ARP. Please note that the PR interval in the PAC with LBBB pattern is longer than the PR interval in the PAC with RBBB pattern as well as the sinus beat. This is due to delay in the AV node which will give enough time for the RBBB to recover and transition LBBB to ARP.

The RBBB pattern is commonly seen compared to a LBBB pattern because of the longer refractory period of the right bundle branch. This aberration is physiologic and does not require a permanent pacemaker. Suppression of the PACs may be accomplished by titration of a beta-blocker, and if the patient continues to be symptomatic, antiarrhythmic therapy may be considered. Catheter ablation is also an option, but reserved for cases which are refractory to pharmacologic therapy.

Options B and D are incorrect since wide QRS complexes are proceeded with P waves.